Glazing panel with a radiation-reflective coating layer

ABSTRACT

A vehicle is provided with a glazing panel coated with a radiation-reflective coating layer and is adapted to have at least an antenna mounted behind the glazing panel. A window permeable to electromagnetic radiations is incorporated in the coating layer such that its size and design increase the transmission ratio between the antenna inside the vehicle and a base station outside the vehicle.

This invention relates to glazing panels and particularly but notexclusively to a vehicle windscreen having a radiation-reflectivecoating layer provided with a window permeable to electromagneticradiations.

Although the invention is described herein with particular reference tocar windscreens it will be understood that it has applications to othervehicle glazing panels, for example car rear windows and side windows,or train windows.

Coating layers are well known to modify the optical properties of glass,particularly to reduce the proportion of incident solar energy which istransmitted through the glass whilst allowing passage of sufficientvisible light to ensure good visibility. This can reduce overheating ofthe interior of the vehicle in summer and is commonly achieved byreflection of incident solar radiation in the infra-red portion of thespectrum. Infared reflecting and other radiation-reflective coatinglayers may increase the selectivity of the glazing panel i.e. the ratioof the proportion of incident visible radiation transmitted through theglazing to the proportion of incident solar energy transmitted throughthe glazing. Although the invention is described herein with particularreference to infrared reflecting coatings, it will be understood that itis suitable for any radiation-reflective coating layer.

Sensors, emitters or antennas arranged inside a car may rely on passageof electromagnetic waves through the windscreen. For example, passage ofan electromagnetic data signal for automatic payment at the toll gatesused on the motorways may pass through the windscreen. However, passageof such electromagnetic signals may be hindered by the presence of aradiation-reflective coating and, consequently, a window in the form ofa gap or hole may be provided in a radiation-reflective coating layerspecifically to allow the passage of electromagnetic radiations throughthat portion of the glazing. This principle is applicable to allowingpassage of any electromagnetic wave through a glazing panel, forexample, between an antenna inside the vehicle and a base station,outside the vehicle, which may be, for example, a cellular phonestation, a satellite, a television/radio emitter, or a short rangecommunication device, such as a toll connection gate or another vehicle.The term window permeable to electromagnetic radiations as used hereinrefers to a portion of the surface area of a glazing adapted to permitelectromagnetic transmission therethrough. Typical electromagnetic wavefrequencies are, for example, 88-108 MHz, 540-1650 kHz, 150-280 kHz forradio signals; 890-960 MHz, 1710-1880 MHz, 1900-2170 MHz, for mobilephone communications; 1575.42±10 MHz for GPS; and 5.8 GHz for DedicatedShort Range Communications.

A “transmission ratio” may be evaluated between an antenna and a basestation. It quantifies the ratio between the intensity received by theantenna under test (AUT) and the intensity received by the same antennaplaced behind a standard uncoated glazing panel, both intensities beingevaluated under the same conditions. The standard uncoated glazing panelpresents a laminated structure: glass (2.1 mm)/PVB (0.76 mm)/glass (2.1mm). Therefore the transmission ratio equals 0 dB if the AUT consists ofthe same antenna placed behind the standard uncoated glazing panel Ifthe transmission ratio is evaluated in air, i.e. without any obstacle,it will be positive, because the signal Is neither reflected norabsorbed by this standard glazing panel. However, if the AUT includesthe antenna placed behind an equivalent glazing panel but comprising afull coating (i.e. without window permeable to electromagneticradiations), the transmission ratio will reach a strong negative leveldue to the reflection and absorption properties of the coated glazing.

The transmission ratio is generally evaluated at 0°, i.e. in a directionnormal to the plane of the AUT and the plane of the base stationantenna. For some applications, the transmission ratio may be evaluatedat +35° or −35°, i.e. in directions forming an angle of 35° on bothsides of direction 0°, when the AUT is rotated in its azimuthal planeunder a constant elevation.

The purpose of providing a coated glazing panel with a window permeableto electromagnetic radiations has always been to reduce the decrease ofthe transmission ratio of the signal going through the glazing panel dueto the radiation-reflective coating layer. However, we have surprisinglyfound that it is possible not only to reduce the decrease of thetransmission ratio but also to improve the transmission ratio, comparedto the transmission through a windscreen without a coating layer andeven, in some cases, to improve it compared to the transmission ratio inair.

According to one aspect, the present invention provides a glazing panelas defined in claim 1. The increase of the transmission ratio asexpressed in claim 1 is evaluated by comparison with an uncoated glazingpanel presenting an equivalent structure, i.e., for example, samethickness of glass, same PVB thickness if the panel is laminated.

This may be used to allow electromagnetic radiations to pass through acoated glazing panel without decreasing the intensity of the radiatedsignal.

In the particular case of a 5.8 GHz circularly polarised wavecommunication between a base station and an antenna inside a vehicle,for example at an electronic toll gate, the transmission ratio at 0°between the base station and the antenna inside the vehicle may beimproved by at least 2 dB, and preferably by at least 5 dB, and thetransmission ratio at ±35° may stay at the same level or may beimproved, compared to the transmission ratios through a glazing panelwithout a coating layer.

The radiation-reflective coating layer may be a sputtered depositedcoating, for example having the general structure antireflectivedielectric layer/optional barrier layer/silver containing conductivelayer/optional barrier layer/antireflective dielectric layer/optionalbarrier/silver containing conductive layer/optional barrierlayer/antireflective dielectric layer. Such coatings are used inautomotive glazings to increase the selectivity of the glazing (i.e. theratio of the proportion of visible light transmitted to the proportionof incident solar energy transmitted) to reduce the solar heating orgreenhouse effect in the vehicle. Alternatively, the coating layer mayhave a single silver containing layer of the general structureantireflective dielectric layer/optional barrier layer/silver containingconductive layer/optional barrier layer/antireflective dielectric layer.A further possibility is for the coating layer to comprise apyrolytically deposited layer based, for example on doped tin oxide.

The radiation-reflective coating layer may be sandwiched between twosheets of glass or it may be an exposed coating layer, for example on amonolithic glazing panel. The coating layer may be deposited directly ona surface of the glazing or it may be carried on a film, for example afilm of PET incorporated in the glazing.

The antenna inside the vehicle is preferably positioned at a distance ofat most $\frac{2D^{2}}{\lambda}$from the glazing panel, where D is the largest dimension of the insideantenna and λ the wavelength of the transmitted electromagnetic wavebetween the base station and the inside antenna, or the wavelength atwhich the antenna is adapted to work In this particular configuration,the glazing panel may act under the physics law of the near-field zoneof antennas, and the transmission ratio may be increased.

Several configurations, shapes, designs and sizes of windows permeableto electromagnetic radiations may be suitable according to the presentinvention.

Preferably, the window permeable to electromagnetic radiations is aportion of the windscreen that does not have the radiation-reflectivecoating layer or is a portion of the windscreen wherein the coatinglayer is absent from a pattern of dots. These dots form uncoatedapertures in the coating layer. The window permeable to electromagneticradiations may be entirely surrounded by the coating layer or may bebounded to the edge of the glazing panel where no coating layer ispresent and thus be partially surrounded by the radiation-reflectivecoating layer.

The glazing panel may comprise several windows permeable toelectromagnetic radiations. This allows several antennas, sensors oremitters to be placed behind the glazing panel, inside the vehicle.Furthermore, windscreens may be provided with at least two windowspositioned symmetrically on both sides of an axis Y₀ which divides theglazing panel along its largest dimension in two equal parts, so as tobe mounted indifferently on cars fitted for left-hand drive orright-hand drive.

The window permeable to electromagnetic radiations may have a size andshape such that at least a square of 1.064λ×1.064λ may be inscribed init, or preferably, at least a square of 5.5×5.5 cm² may be inscribed init. λ is the wavelength of the transmitted electromagnetic wave betweenthe base station and the inside antenna.

Alternatively, the window permeable to electromagnetic radiations may bea substantially circular zone having an area of at least 0.735λ², orpreferably, at least 19.5 cm². It may be a disk with a diameter of atleast 1.354λ, or preferably, a disk with a diameter of at least 7 cm.

Where the window permeable to electromagnetic radiations is a portion ofthe windscreen wherein the coating layer is absent from a pattern ofdots, the dots may be arranged linearly or in alternate rows.Preferably, the dots have substantially the same size. Such a patternmay be particularly favourable to the increase of the transmission ratiothrough the window. Indeed, it has been found that the pattern of dotsmay increase the directivity of the transmission by focusing the signal,and may also increase the efficiency of the transmission by improvingthe polarisation, the latter being particularly true when consideringcircularly polarised waves.

Advantageously the dots without coating layer have each a diameter of atleast 0.116λ. Preferably, the dots without coating layer have each adiameter of at least 5 mm, or between 5 and 7 mm, or still preferably, 6mm.

The window permeable to electromagnetic radiations may comprise at least50 dots with no coating layer, and preferably at least 64 dots with nocoating layer. This may optimise the increase in the transmission ratio,so that the transmission ratio may even be higher than the transmissionratio in air, i.e. without glazing panel to pass through. With 64 dots,a maximum transmission ratio may be reached and there may be no furtherimprovement if further dots are added.

Many radiation-reflective coating layers have the intrinsic property ofbeing electrically heatable. The vehicle glazing panel according to thepresent invention may indeed be heated to be de-misted or de-iced. It isdesired that the heating of the glazing panel be as uniform as possible,avoiding hot spots which may damage the coating layer, and avoiding lowtemperature zones where a de-icing or de-misting function may bedelayed. The preferred particular pattern of dots without coating layerin the window permeable to electromagnetic radiations allow the glazingpanel to be heated substantially uniformly, but other shapes and designsof windows are also suitable to obtain a homogeneous heating pattern.

Embodiments of the invention will now be described, by way of examplesonly, with reference to FIGS. 1 and 2.

FIG. 1 shows a car windscreen and an enlargement of a portion around thewindow permeable to electromagnetic radiations.

FIG. 2 shows other suitable patterns for the window permeable toelectromagnetic radiations.

Several transmission ratios have been measured and compared to thetransmission ratio through a glazing panel without a coating layer,which served as the reference and to which we gave a value of 0 dB.Results are given in the table below. The electromagnetic waves analysedin this example were all dedicated short range communications at 5.8 GHzas can be found at electronic toll gates on motorways. These arecircularly polarised waves. The distance between the antenna inside thevehicle and the glazing panel was in all cases 18 mm, and the largestdimension of the antenna inside the vehicle was approximately 30 mm.

When analysing transmissions at 0°, It shows that when the signal passesthrough a coated glazing with a window permeable to electromagneticradiations which is a disk of 50 mm diameter without coating layer or arectangle of 120×70 mm² without coating layer, the transmission ratio isIncreased by 2 dB, compared to a signal passing through a glazingwithout coating layer. Similarly, the transmission is increased by 5 dB,when the signal does not pass through a glazing panel, i.e. in the air.Finally, the transmission ratio is increased by 7 dB when the signalpasses through a window permeable to electromagnetic radiations which isa square of 6×6 cm² comprising 64 dots without coating layer of 6 mmdiameter each. In this particular embodiment, the transmission ratio isthus better than in the air. As counterexample, the transmission ratiois decreased by 6 dB when the signal passes through a window permeableto electromagnetic radiations which is a square of 6×6 cm² comprising 64crosses without coating layer of 6 mm long and 1 mm broad. The case of awindscreen with a coating layer which does not comprise a windowpermeable to electromagnetic radiations is also mentioned in the table:the transmission ratio is in that case decreased by 20 to 40 dB,compared to a windscreen without coating layer.

When analysing transmissions at ±35°, the reference selected is also aglazing panel without coating layer. When the signal passes through awindow permeable to electromagnetic radiations which Is a square of 6×6cm² comprising 64 dots without coating layer of 6 mm diameter each, thetransmission ratio is at the same level than the reference: it isneither decreased nor increased. Like in the transmission at 0°, thetransmission at ±35° is increased by 5 dB, when the signal does not passthrough a glazing panel, i.e. in the air. When the signal passes througha coated glazing with a window permeable to electromagnetic radiationswhich is a rectangle of 120×70 mm² without coating layer, thetransmission ratio is increased by 1 dB. Transmission Transmission at 0°at ±35° Pattern of dots without coating layer +7 dB  0 dB No windscreen(air) +5 dB +5 dB 120 × 70 mm² rectangle without +2 dB +1 dB coatinglayer 50 mm disk without coating layer +2 dB REFERENCE: Windscreenwithout coating layer  0 dB  0 dB Pattern of crosses without coatinglayer −6 dB Windscreen with IR reflecting coating −20 to −40 dB layer

FIG. 1 shows a car windscreen 1 having a radiation-reflective coatinglayer 2 and a window permeable to electromagnetic radiations 3. Thewindow permeable to electromagnetic radiations is a square of 6×6 cm²comprising 64 dots without coating layer 4. Each dot has a diameter of 6mm and is separated from the neighbouring dots by a distance of 1 mm.

FIG. 2 shows other suitable patterns for the window permeable toelectromagnetic radiations. FIG. 2 a shows a circular window of 7 cm indiameter comprising 76 dots of 6 mm in diameter, arranged in alternaterows. FIG. 2 b shows a circular window of 7 cm in diameter comprising 76dots of 6 mm in diameter, arranged linearly.

1. A vehicle glazing panel comprising a radiation-reflective coatinglayer and at least a window in the coating layer, permeable toelectromagnetic radiations, adapted to have at least an inside antennamounted behind it, characterised in that the size and design of thewindow permeable to electromagnetic radiations increase the transmissionratio at 0° between said inside antenna and a base station outside thevehicle. 2-18. (canceled)
 19. A vehicle glazing panel in accordance withclaim 1, characterised in that, when considering a circularly polarisedelectromagnetic wave of 5.8 GHz, the size and design of the windowpermeable to electromagnetic radiations: (a) increase the transmissionincrease the transmission ratio at 0° between the inside antenna and thebase station by at least 2 dB; or (b) increase the transmission ratio at0° between the inside antenna and the base station by at least 5 dB; or(c) do not decrease the transmission ratio at +35° or −35° between theinside antenna and the base station.
 20. A vehicle glazing panel inaccordance with claim 19, characterised in that it includes feature (c)and one of features (a) or (b).
 21. A vehicle glazing panel inaccordance with claim 1, characterised in that the distance between theposition at which the inside antenna is adapted to be mounted and theglazing panel is at most 2D²/λ, where D is the largest dimension of theinside antenna and λ the wavelength to which the antenna is devoted. 22.A vehicle glazing panel in accordance with claim 19, characterised inthat the distance between the position at which the inside antenna isadapted to be mounted and the glazing panel is at most 2D²/λ, where D isthe largest dimension of the inside antenna and λ the wavelength towhich the antenna is devoted.
 23. A vehicle glazing panel in accordancewith claim 1, characterised in that the window permeable toelectromagnetic radiations has a size (a) such that at least a square of1.064λ×1.064λ may be inscribed in it, wherein λ is the wavelength towhich the antenna is devoted, or (b) such that at least a square of5.5×5.5 cm² may be inscribed in it.
 24. A vehicle glazing panel inaccordance with claim 1, characterised in that the window permeable toelectromagnetic radiations is (a) a substantially circular zone havingan area of at least 0.735λ², wherein λ is the wavelength to which theantenna is devoted, or (b) is a substantially circular zone having anarea of at least 19.5 cm², or (c) a disk with a diameter of at least 7cm.
 25. A vehicle glazing panel in accordance with claim 1,characterised in that the window permeable to electromagnetic radiationsis (a) a zone wherein no coating layer is present, or (b) a zone whereinthe coating layer is absent from a pattern of dots arranged linearly, or(c) a zone wherein the coating layer is absent from a pattern of dotsarranged in alternate rows, or (d) a zone wherein the coating layer isabsent from dots each having a diameter of at least 0.116λ, wherein λ isthe wavelength to which the antenna is devoted, or (e) a zone whereinthe coating layer is absent from dots each having a diameter of at least5 mm, or (f) a zone wherein the coating layer is absent from dots eachhaving a diameter between 5 and 7 mm, or (g) a zone comprising at least50 dots wherein the coating layer is absent; or (h) a zone comprising atleast 64 dots wherein the coating layer is absent.
 26. A vehicle glazingpanel in accordance with claim 1, which is electrically heatable.
 27. Avehicle glazing panel in accordance with claim 19, which is electricallyheatable.
 28. A vehicle glazing panel in accordance with claim 21, whichis electrically heatable.
 29. A vehicle glazing panel in accordance withclaim 23, which is electrically heatable.
 30. A vehicle glazing panel inaccordance with claim 24, which is electrically heatable.
 31. A vehicleglazing panel in accordance with claim 25, which is electricallyheatable.